Cancers are difficult to cure even at the present day, and hence inflict great pains and economical losses on the world. Broadly speaking, a cancer is treated by three therapies of radiotherapy, chemotherapy and surgical therapy.
In the radiotherapy for the cancer among these, the presence of hypoxic cells in the tumor becomes the greatest problem. The hypoxic cells have high resistance to radioactive rays and are hence believed to be a serious cause of the refractoriness and/or the recurrence in the radiotherapy. On the other hand, no hypoxic cells exist in any normal tissues. Upon performing the radiotherapy for the cancer, it is therefore important to enhance the radiosensitivity of the hypoxic cells in the tumor.
In view of the foregoing circumstances, the present inventors carried out an extensive investigation with a view toward providing a medicament by which the radiosensitivity of normal cells is unchanged and only hypoxic cells are sensitized when radiotherapy is performed, i.e., a radiosensitizer for hypoxic cells (hereinafter referred to as "radiosensitizer"). As a result, it has been found that a 2-nitroimidazole derivative represented by the general formula (I) which will be described subsequently has a high radiosensitizing effect even in a low concentration and is also low in toxicity which has heretofore become the greatest problem, leading to completion of the present invention.